when I try to combine two pdf's, it asks for a permission password and says the documents are protected; however, I didn't put any protection/security in the documents. I assume it is a default security under the enhanced security settings of the Acrobat

When I try to combine two pdf's, it asks for a permission password and says the documents are protected; however, I didn't put any protection/security in the documents.  I assume it is a default security under the enhanced security settings of the Acrobat Pro XI which I recently purchased.